The invention concerns a measurement chip for carrying out measurements of transmission and/or emission and/or scattering of light by a fluid sample in an operator device and a corresponding measurement system which includes the measurement chip and the operator device. Analytical measurement devices for transmission, emission or scattering measurements on liquid or gaseous samples (fluid samples) are known in the most widely varying design configurations. One use of such measurement devices is that of determining the concentration of an analyte in a fluid sample. For that purpose a fluid sample is introduced into a measurement cell and the concentration of an analyte to be determined is measured on the basis of the absorption or transmission of a coupled-in light beam or on the basis of the emission of light which is delivered by the sample by virtue of fluorescence, luminescence, chemiluminescence or scattering. The absorption or emission of light can be produced or caused by the analyte itself or by another substance which is present in the sample, in dependence on the concentration of the analyte.
Chemical or enzymatic color reactions are frequently used in bio and environmental analysis for determining the concentration of analytes. In dependence on the concentration of the analyte to be investigated, a substrate is chemically or enzymatically converted into a product which has absorption or fluorescence properties which are altered in relation to the initial substrate. Light is coupled into a measurement cell which contains the product and the absorption or transmission of the light which is coupled in or a fluorescence emission caused by the coupled-in light is measured. The measured absorption or transmission or fluorescence is in a direct relationship with the concentration of the analyte to be investigated.
Various methods and devices are used depending on the respective task to be performed. A laboratory standard device is the fluorescence spectrometer which as measurement cells uses cuvettes for receiving fluid samples.
One problem with measurement using conventional fluorescence spectrometers is that only a fraction, about ⅙th, of the emitted fluorescence radiation is measured as light is radiated radially from a sample but the detector is usually arranged only on one side of the sample or the measurement cell. Those spectrometers either have a low level of sensitivity or require photomultipliers which boost the low level of radiation. To overcome the problem of low sensitivity in other known devices many detectors are distributed around the sample or the measurement cell to receive as much emitted radiation as possible. That however is very complicated and expensive.
A further use of analytical measurement devices is position-resolving measurement of fluorescence or angle-dependent measurement of scatter radiation. For example in environmental analysis the proportion of colloid in water samples is determined in accordance with standardised measurement methods on the basis of the angles at which scattering maxima occur or on the basis of the ratios of scatter light intensities with various predetermined scatter angles. Angle-resolving scatter measurements are required for the samples for that purpose. Known devices for angle-dependent fluorescence or scattering measurement use either a large number of detectors which are arranged in fixed measurement angles around the measurement cell, or they use a goniometer in which a detector fixed to a rotating arm is moved over an angular range around the measurement cell. Those apparatuses are highly complicated and expensive in terms of the apparatus involved, costly and take up a great deal of space. They are entirely inappropriate for mobile use.
EP 1 494 007 A1 describes a multi-wave system for fluorescence or absorption measurement, in which deflection of the incident light beam at a mirror ensures that only the light which is given off by the sample or which passes through the sample reaches a detector, but not the incident light. The direction of the incident light is parallel to that of the emitted light. With that apparatus, fluorescence measurement suffers from the disadvantage already described hereinbefore, that only a fraction of the irradiated fluorescence light reaches the detector.
U.S. Pat. No. 4,154,233 describes an apparatus for transmission measurement on fluids using a sample vessel having a V-shaped reflecting bottom. The beam paths of the incident light and the emergent light are parallel. By virtue of reflection at the V-shaped bottom the light passes over a longer distance through the fluid. The apparatus is not suitable for the measurement of light emission or scattering.
EP 1 247 577 A2 discloses a method of detecting whether a liquid or a gas is being passed in a micro-passage system. In that system, a micro-passage is deflected in such a way that two reflection surfaces are produced at the passage walls, which are at an angle of 90° relative to each other. Disposed between the reflection surfaces is a transparent substrate material. If light which is coupled in from a light source impinges on the first reflection surface at an angle of 45°, it is reflected at an angle of 90° to the second reflection surface and is again reflected thereby at an angle of 90° to a detector. The reflection surfaces are totally reflective if the micro-passage is carrying gas so that almost all the light from the light source also arrives at the detector. If the micro-passage is carrying liquid then the surfaces are not totally reflective so that less or no light from the light source reaches the detector. The light arriving at the detector indicates whether the micro-passage is carrying gas or liquid.
U.S. Pat. No. 5,599,503 discloses a miniaturised detector cell in which incident light is reflected a plurality of times within a measurement distance in order even when dealing with small samples to ensure contact which is as long as possible for the incident light with the sample.
DE 102 45 845 discloses a measurement chip having a plurality of pyramid-shaped raised portions in the measurement zone, which serve to increase the surface area and thus to enhance the light intensity for the measurement.